CT Traceability - Calibration and Accuracy Calibration and Accuracy - - PowerPoint PPT Presentation

▶
ct traceability calibration and accuracy calibration and
SMART_READER_LITE
LIVE PREVIEW

CT Traceability - Calibration and Accuracy Calibration and Accuracy - - PowerPoint PPT Presentation

Mar 25, 2024 379 likes •1.03k views

CT Traceability - Calibration and Accuracy Calibration and Accuracy Prof. Wim Dewulf, Group T - KU Leuven Outline Introduction: terminology and procedures Voxel size calibration Edge offset calibration Conclusions Outline

slide-1
SLIDE 1

CT Traceability - Calibration and Accuracy Calibration and Accuracy

  • Prof. Wim Dewulf, Group T - KU Leuven
slide-2
SLIDE 2

Outline

  • Introduction: terminology and procedures
  • Voxel size calibration
  • Edge offset calibration
  • Conclusions
slide-3
SLIDE 3

Outline

  • Introduction: terminology and procedures
  • Voxel size calibration
  • Edge offset calibration
  • Conclusions
slide-4
SLIDE 4

CT metrology: no resolution, but accuracy

  • Medical and material applications are satisfied with resolution
  • Dimensional metrology requires accuracy and traceability to the unit of length

(the meter) Required accuracy:

  • Medical and material applications: none or 10-1-10-2 (1..5%)
  • Dimensional metrology: CMM 10-5-10-6 (laserinterferometry 10-7-10-8)
  • µ

µ µ

µ µ !µ "#!$

µ

slide-5
SLIDE 5

Resolution

slide-6
SLIDE 6

Traceability

slide-7
SLIDE 7

CT metrology procedure

CT scan Data Processing 3D Reconstruction (CT Pro) Object 2D X-ray images 3D grey voxel model Data Analysis Dimensional measurement (VolumeGraphics) Thresholding Edge detection (VolumeGraphics) Surface model Dimensions

slide-8
SLIDE 8

Influencing parameters

slide-9
SLIDE 9

Two main questions

?

Voxel size Edge

?

slide-10
SLIDE 10

Outline

  • Introduction: terminology and procedures
  • Voxel size calibration
  • Edge offset calibration
  • Conclusions
slide-11
SLIDE 11

Voxel size calibration

Influence of workpiece position

1 µm 2 µm

slide-12
SLIDE 12

Voxel size calibration

Calibration with traceable reference objects

slide-13
SLIDE 13

Voxel size calibration

Calibration with traceable reference objects Excellent repeatability

slide-14
SLIDE 14

4,002

en spheres [mm]

Repeatability of distance between spheres

Voxel size calibration

Calibration with traceable reference objects Repeatability

4,001 2 4 6 8

Distance between s

slide-15
SLIDE 15

Voxel size calibration

Calibration with traceable reference objects Repeatability

2.998 2.999

Sphere center distance [mm]

2.995 2.996 2.997 1 2 3 4 5 Measurement n°

slide-16
SLIDE 16

Voxel size calibration

Calibration with traceable reference objects Repeatability

slide-17
SLIDE 17

Voxel size calibration

Calibration by combining CT and CMM

slide-18
SLIDE 18

Voxel size calibration

Calibration by combining CT and CMM

slide-19
SLIDE 19

Voxel size calibration

Calibration by combining CT and CMM

slide-20
SLIDE 20

Voxel size calibration

Calibration by combining CT and CMM

slide-21
SLIDE 21

Repeatability

Spreiding van 30 metingen in software (VG)

4,9610 4,9620 4,9630 4,9640 arde [mm] mean value measurements

  • 1 sigma

+1 sigma

value (mm) Repeatability of data processing: 2D-3D reconstruction (CT-pro), automatic edge detection and plane-plane measurement (Volume Graphics)

(30 measurements in software)

Voxel size calibration

Calibration by combining CT and CMM

4,9570 4,9580 4,9590 4,9600 Meetwaarde

σ ≈ ≈ ≈ ≈ 1µm

Measured v Repeatability including data acquisition: Range: 15 µm (at 35µA, 180kV) 30 µm (for 45µA and voltage varying from 160 to 190 kV)

Range ≈ ≈ ≈ ≈ 5.7µm ≈ ≈ ≈ ≈ 3σ

(5 measurements in approx. same conditions: temperature, time of day and machine warm-up, but no temperature controlled room)

slide-22
SLIDE 22

Influences on the voxel size

Drift of X-ray source

Source: Vogeler et al., 2011

slide-23
SLIDE 23

Influences on the voxel size

Drift of X-ray source

Source: Vogeler et al., 2011

slide-24
SLIDE 24

Influences on the voxel size

Tilt of detector and/or rotation stage

slide-25
SLIDE 25

Influences on the voxel size

Tilt of detector and/or rotation stage

slide-26
SLIDE 26

Outline

  • Introduction: terminology and procedures
  • Voxel size calibration
  • Edge offset calibration
  • Conclusions
slide-27
SLIDE 27

Edge offset calibration

Edge detection

Partial volume effect

slide-28
SLIDE 28

Edge offset calibration

Edge detection

Material Background ISO50%

slide-29
SLIDE 29

Edge offset calibration

Edge detection

slide-30
SLIDE 30

Edge offset calibration

slide-31
SLIDE 31

Edge offset calibration

slide-32
SLIDE 32

Edge offset calibration

32

slide-33
SLIDE 33

Edge offset calibration

33

slide-34
SLIDE 34

Edge offset calibration

Edge detection

Material Background Edge ISO50%

slide-35
SLIDE 35

0.020 0.040 0.060

MM - CT) [mm]

Afwijking t.o.v. meting met CMM i.f.v. grijswaarde voor de rand

automatische rand

Deviation compared to CMM measurements for different grey values

measurements

Automatic e detection

Edge offset calibration

  • 0.060
  • 0.040
  • 0.020

0.000 27500 28000 28500 29000 29500 30000 30500 31000 31500 32000

Afwijking t.o.v. meting met CMM (CMM Grijswaarde voor randdetectie

56D 47D 39D 48D

anddetectie (= ISO50%)

Deviation compared to CMM m [mm] Grey value for edge detection

edge ion

slide-36
SLIDE 36

Edge offset calibration

Calibration by combining CT and CMM

slide-37
SLIDE 37

Edge offset calibration

Calibration by combining CT and CMM

Source: Carmignato et al., 2009

slide-38
SLIDE 38

Edge offset calibration

Calibration by combining CT and CMM

38

slide-39
SLIDE 39

Edge offset calibration

Advanced edge detection

slide-40
SLIDE 40

0.020 0.040 0.060

MM - CT) [mm]

Afwijking t.o.v. meting met CMM i.f.v. grijswaarde voor de rand

automatische rand

Deviation compared to CMM measurements for different grey values

measurements

Automatic e detection

Edge offset calibration

  • 0.060
  • 0.040
  • 0.020

0.000 27500 28000 28500 29000 29500 30000 30500 31000 31500 32000

Afwijking t.o.v. meting met CMM (CMM Grijswaarde voor randdetectie

56D 47D 39D 48D

anddetectie (= ISO50%)

Deviation compared to CMM m [mm] Grey value for edge detection

edge ion

40

slide-41
SLIDE 41

Edge offset calibration

Calibration workpieces

slide-42
SLIDE 42

Edge offset calibration

Calibration workpieces

slide-43
SLIDE 43

Edge offset calibration

Influence of workpiece properties (e.g. material, roughness,…)

Optical Tactile

slide-44
SLIDE 44

Edge offset calibration

Influence of spot size and workpiece position

slide-45
SLIDE 45

Edge offset calibration

Influence of feature orientation

slide-46
SLIDE 46

No BHC

Edge offset calibration

Influence of source settings

slide-47
SLIDE 47

Initial spectrum

Edge offset calibration

Influence of beam hardening

After e.g. 1mm

slide-48
SLIDE 48

Edge offset calibration

Influence of beam hardening

slide-49
SLIDE 49

Edge offset calibration

Influence of beam hardening

slide-50
SLIDE 50

Reconstructed slice

Edge offset calibration

Influence of beam hardening

slide-51
SLIDE 51

Edge offset calibration

Influence of beam hardening

slide-52
SLIDE 52

Edge offset calibration

Influence of beam hardening

Source: Wenig et al., 2006

slide-53
SLIDE 53

Edge offset calibration

Influence of beam hardening

Source: Wenig et al., 2006

slide-54
SLIDE 54

Edge offset calibration

Influence of beam hardening

slide-55
SLIDE 55

Edge offset calibration

Influence of beam hardening

slide-56
SLIDE 56

Inwards

  • ffset

Edge offset calibration

Influence of beam hardening

slide-57
SLIDE 57

Edge offset calibration

Influence of beam hardening

slide-58
SLIDE 58

Edge offset calibration

Influence of beam hardening

slide-59
SLIDE 59

Edge offset calibration

Multi-material objects

Number (Source: Shammaa et al., 2010) Grey value

slide-60
SLIDE 60

Edge offset calibration

Multi-material objects

Steel Steel Advanced calibration method (local thresholding) Thresholding

  • n 1

greyvalue Ceramic Ceramic

slide-61
SLIDE 61

Outline

  • Introduction: terminology and procedures
  • Voxel size calibration
  • Edge offset calibration
  • Conclusions
slide-62
SLIDE 62

Conclusions

  • Traceability of CT is challenging
  • Influencing factors relate to CT device, measurement

procedure, data processing, object, and environment

  • Good measurement procedures, including calibration of

both voxel size and edge offset, can reduce measurement uncertainties by a factor 5-10